DIODE CHARACTERISTICS

1-27 Figure 1-24.—Basic diode switch. When the input to this circuit is at zero potential, the diode is forward biased because of the zero potential on the cathode and the positive voltage on the anode. In this condition, the diode conducts and acts as a straight piece of wire because of its very low forward resistance. In effect, the input is directly coupled to the output resulting in zero volts across the output terminals. Therefore, the diode, acts as a closed switch when its anode is positive with respect to its cathode. If we apply a positive input voltage (equal to or greater than the positive voltage supplied to the anode) to the diode’s cathode, the diode will be reverse biased. In this situation, the diode is cut off and acts as an open switch between the input and output terminals. Consequently, with no current flow in the circuit, the positive voltage on the diode’s anode will be felt at the output terminal. Therefore, the diode acts as an open switch when it is reverse biased. Q27. What is a load? Q28. What is the output of a half-wave rectifier? Q29. What type of rectifier is constructed by sandwiching a section of semiconductor material between two metal plates? Q30. What type of bias makes a diode act as a closed switch? DIODE CHARACTERISTICS Semiconductor diodes have properties that enable them to perform many different electronic functions. To do their jobs, engineers and technicians must be supplied with data on these different types of diodes. The information presented for this purpose is called DIODE CHARACTERISTICS. These characteristics are supplied by manufacturers either in their manuals or on specification sheets (data sheets). Because of the scores of manufacturers and numerous diode types, it is not practical to put before you a specification sheet and call it typical. Aside from the difference between manufacturers, a single manufacturer may even supply specification sheets that differ both in format and content. Despite these differences, certain performance and design information is normally required. We will discuss this information in the next few paragraphs.